Ongoing experiments aimed at characterizing the behavioral pharmacology of narcotic antagonists and morphine will be continued and expanded upon with the major emphasis on the systematic and quantitative assessment of the discriminative stimulus properties of these drugs. Representative narcotic antagonists, narcotic agonists, and non-opioid psychoactive drugs will be tested in rats and squirrel monkeys trained to discriminate between saline and morphine or between saline and cyclazocine, thus permitting interspecies as well as intraspecies comparisons of drugs as discriminative stimuli. Discriminative stimuli associated with the narcotic withdrawal syndrome will be evaluated in morphine-dependent rats trained to discriminate between the administration of saline and the narcotic antagonist naltrexone. Experiments involving intracerebral drug administration and drug interactions will be performed in an effort to define the receptor populations and neuroanatomical sites subserving the stimulus control of behavior by narcotic antagonists and agonists. If the components of action of narcotic antagonists and agonists which enable them to function as discriminative stimuli in the rat and squirrel monkey are found to be related to the components of action that engender subjective effects in man, it should be possible to develop animal models for identifying and studying the properties of these drugs that underlie their abuse potential.